Lubricant compositions

ABSTRACT

SYNTHETIC ESTER LUBRICATING OIL COMPOSITIONS CONTAINING MINOR AMOUNTS OF (1) A TRIHYDROCARBYL PHOSPHATE, (2) AN ALKYL AMINE SALT OF A MONOHALKYLPHOSPHONIC ACID AND (3) A DICARBOXYLIC ACID HAVE IMPORVED ANTICORRROSION, ANTIOXIDATION AND LOAD-CARRYING PROPERTIES.

United States Patent 3,634,239 LUBRICANT COMPOSITIONS Alexander C. B. MacPhail, Cheshire, England, and John E. Lauck, Godfrey, and Kenneth T. Wendler, Alton, Ill.,

assignors to Shell Oil Company, New York, N.Y.

No Drawing. Filed Sept. 8, 1969, Ser. No. 856,159 Int. Cl. Cltlm 1/46 U.S. Cl. 252--32.5 9 Claims ABSTRACT OF THE DlSOLUSURE This invention relates to synthetic ester lubricating oils having excellent corrosion resistance, oxidation stability and load-carrying properties. More particularly it relates to synthetic ester oils containing a combination of 1) a trihydrocarbyl phosphate, (2) an alkyl amine salt of a monohaloalkylphosphonic acid and (3) a dicarboxylic acid.

Synthetic ester base oils are particularly suitable for use in high temperature-high speed lubricating applications such as in the lubrication of gas turbine engines because of their inherently good thermal stability and desirable viscosity properties. Although ester base lubricants are superior to mineral lubricating oils in many respects, they have a tendency to be slightly more corrosive and Will undergo oxidation and decompose at elevated temperatures. It is known that the thermal decomposition of synthetic ester oils is significantly accelerated by the presence of minute quantities of dissolved metals such as iron which can result from the dissolution of steel components by the ester base stocks or additives incorporated into these oils.

Concern over the problem of corrosion and catalytic degeneration is reflected in the recently proposed military specification for aircraft gas turbine lubricants, MIL-L- 23699B. This specification contains a number of tests directed to evaluating the corrosivity and oxidation-resistance of lubricating fluids, including a newly developed Naval Thermal Stability-Corrosivity test. The demands placed on lubricating oils by this specification are extremely stringent, and only compositions possessing exceptional properties can qualify. Such lubricant compositions are the subject of the present invention.

It has now been found that lubricant compositions comprising a major amount of a synthetic ester lubricating oil and minor amounts each of (l) a trihydrocarbyl phosphate, (2) an alkyl amine salt of a monohaloalkylphosphonic acid and (3) a dicarboxylic acid have excellent anticorrosion, antioxidation and load-carrying properties. The aforementioned compositions have been found to be remarkably effective in passivating steel surfaces, thus substantially preventing dissolution of the metal, which correspondingly also increases the oxidation stability of the oil. In addition, the present compositions have been found to possess excellent load-carrying properties and are eminently suited for use in high temperature-high speed lubricating applications.

The hydrocarbyl groups can be alkyl, aryl, alkaryl and templated for use in the present compositions include those represented by the formula:

3,634,239 Patented Jan. 11, 1972 wherein R R and R are the same or different hydrocarbyl groups having from 1 to about 15 carbon atoms. The hydrocarbyl groups can be alkyl, aryl, alkaryl and aralkyl radicals. Aryl or alkaryl groups having from 1 to 10 carbon atoms are especially preferred.

Examples of suitable trihydrocarbyl phosphate compounds include tricresyl phosphate, tri(2,4-dimethylphenyl) phosphate, tri-(p-ethylphenyl) phosphate, tri-(Z-methyl-4-isopropylphenyl) phosphate, tri(p-tert butylphenyl) phosphate, tri-(2,6 dimethyl 4-tert-butylphenyl) phos phate, tri (4 methyl-l-naphthyl)phosphate, ethyl di- (p-cresyl) phosphate, 2,6-xylenyl di-(n-butyl) phosphate, triphenyl phosphate, cresyl diphenyl phosphate, dicresyl phenyl phosphate, xylyl dicresyl phosphate, trixylyl phosphate, dimethyl xylyl phosphate, dimethyl tolyl phosphate, dimethyl phenyl phosphate, methyl diphenyl phosphate, octyl diphenyl phosphate, trimethyl phosphate, triethyl phosphate, tri-n-butyl phosphate, tris(2-ethyl hexyl) phosphate, and mixtures thereof. Of the foregoing, tricresyl phosphate has been found to be particularly advantageous for use in the compositions of the invention.

Amine salts which are suitable for use in the present compositions are the salts of C alkyamines and monohaloalkylphosphonic acids. Haloalkylphosphonic acid which can be used in forming these salts have the .general formula wherein R is a monohaloalkyl group containing 1 to 4, preferably 1 to 2 carbon atoms. Preferred halogens are fluorine, chlorine and bromine. Acids wherein the R group contains a chlorine atom substituted on the alpha carbon atom are especially advantageous for the purposes of the invention. Examples of such acids, include monochloromethylphosphonic acid, u-monochloroethylphosphonic acid, a-monochloropropylphosphonic acid, oc-ChlO- ro-u-methyl-ethylphosphonic acid, a-chloro-butylphosphonic acid and a-chloro-a-methyl-propylphosphonic acid. The anhydrides of the aforementioned acids can also be 'used to prepare suitable amine salts.

Amines which form eifective salts with the above-described acids are primary or secondary alkyl amines having at least 8, preferably 8 to 30, and more preferably 12 to 24 carbon atoms per molecule. Branched tertiary-alkyl primary amines are preferred; branched in this context means having at least 2 hydrocarbon substituents attached to the main carbon chain. As the tertiary-alkyl radical, the radical of polyisobutylene and polypropylene, and mixtures of these are particularly preferred. Examples of these amines are 1,l,3,3-tetramethylbutylamine, l,l,3,3, 5,S-hexamethylhexylamine, l,l,3,3,5,5,7,7 octamethyloctylamine and 1,1,3,3,5,5,7,7,9,9-decamethyldecylamine. Tertiary alkyl methyl primary amines, such as 2,2,4,4 tetramethylpentylamine and 2,2,4,4,6, 6 hexamethyl hexylamine are also suitable.

Other primary amines having 8 to 30 carbons which are appropriate for forming the salts of the invention are described in Bortnick, US. 2,606,923, issued Aug. 12, 1952, and Bortniclr, US. 2,611,782, issued Sept. 23, 1952. These include tert-tridecylamine,

CgH5 (l-CaH17-C|NH2) as Well as isoheptyl diethyl carbinylamine, isooctylethyl propylcarbinylamine, etc. Primary amines of this type are commercially available from Rohm and Haas Company under the trade name of Primenes. The amine may also be a polyamine, such as a diamine or triamine, and

may contain other non-reactive groups, such as amide or ether groups in the carbon chain.

Some specific examples of secondary amines for making the phosphonic acid salts are diamylamine, dihexylamine, di(2-ethylhexyl)amine, dioctylamine, didecylamine, didodecylamine, ditetradecylamine, dihexadecylamine, dioctadecylamine, dibromodioctadecylamine, isopropyloleylamine, diricinoleylamine, butylricinoleylamine, butyl-2- ethylhexylamine, dilaurylamine, methyloleylamine, ethyloctylamine, isoamylhexylamine, dicyclohexylamine, dicyclopentylamine, cyclohexyloctylamine, cyclohexylabenzylamine, benzyloctylamine, benzyl-Z-ethylhexylamine, allyloctylamine, dodecyl-2-ethyihexylamine, N,N-diallyl trimethylene diamine, 3-hexyl-morpholine, and the like.

The phosphonic acid-amine salts for use in the invention can be prepared by direct neutralization of haloalkylphosphonic acid with a substantially stoichiometric amount of amine. The reaction occurs at normal or moderately elevated temperatures and may be carried out in the presence of an inert diluent or solvent, such as a hydrocarbon, alcohol, ether, ketone, etc. Preparation of these salts is described in Watson et al., US. 2,858,332, issued Oct. 28, 1958.

The phosphonic acid-amine salts useful in the invention may also be modified with an alkali metal as described in Price et al., US. 3,112,267, issued Nov. 26, 1963. The full amine salt of the phosphonic acid is prepared and is then treated in a low-boiling solvent with an alkali metal hydroxide, carbonate, or alcoholate such that one of the amine groups is replaced with an alkali metal. Preferred alkali metals are sodium, potassium, and lithium.

Dicarboxylic acids which can be effectively used in combination with the previously described trihydrocarbyl phosphates and amine salts are those dicarboxylic acids having from 4 to 14 carbon atoms. While it is contemplated that other dicarboxylic acids can be used, aliphatic dicarboxylic acids are preferred. Examples of these include adipic, pimelic, suberic, azelaic, sebacic, brassylic, and the like. Azelaic acid has been found to be particularly effective in the compositions of the invention.

Suitable synthetic lubricant base stocks for the practice of the invention are esters of alcohols having 1 to 20, especially 4 to 12 carbon atoms and aliphatic carboxylic acids having from 3 to 20, especially 4 to 14 carbon atoms. The ester base may comprise a simple ester (reaction product of a monohydroxyalcohol and a monocarboxylic acid) a polyester (reaction product of an alcohol and an acid, one of which has more than one functional group), or a complex ester (reaction product of a polyfunctional acid with more than one alcohol, or of a polyfunctional alcohol with more than one acid). Also, excellent synthetic lubricants may be formulated with mixtures of esters, such as major proportions of complex esters and minor amounts of diesters.

Examples of suitable ester base oils are ethyl palmitate, ethyl laurate, butyl stearate, di-(2ethylhexyl)sebacate, di-(2-ethylhexyl) azelate, ethyl glycol dilaurate, di-(2- ethylhexyl)phthalate, di-(1,3-methylbutyl) adipate, di(1- ethylpropyl) azelate, diisopropyloxylate, dicyclohexyl sebacate, glycerol tri-n-heptoate, di(undecyl) azelate, and tetraethylene glycol di-(Z-ethylene caproate), and mixtures thereof. A preferred mixture of such esters consists of about 50-80% bis (2,2,4-trimethylpentyl) azelate and 20 to 50% 1,1,1-trimethylyl propane triheptanoate.

Especially preferred esters for use as base stocks in the present invention are esters of monocarboxylic acids having 4 to 14 carbons and polyalcohols such as pentaerythritol, dipentaerythritol, and trimethylolpropane. Examples of these esters are pentaerythrityl tetrabutyrate, pentaerythrityl tetravalerate, pentaerythrityl tetracaproate, pentearythrityl dibutyratedicaproate, pentaerythrityl butyratecaproate divalerate, pentaerythrityl butyrate trivalerate, pentaerythrityl butyrate tricaproate, pentaerythrityl tributyratecaproate, mixed C saturated fatty acid esters of pentaerythritol, dipentaerythrityl hexavalerate,

dipentaerythrityl hexacaproate, dipentaerythrityl hexaheptoate, dipentaerythrityl, hexacaprylate, dipentaerythrityl tributyratetricaproate, dipentaerythrityl trivalerate tripelargonate dipentaerythrityl mixed hexaesters of C fatty acids and trimethylolpropane heptoate. Mixtures of C monocarboxylic acid esters of pentaerythritol and dipentaerythritol are particularly advantageous base oils and are commercially available from Hercules, Inc.

The trihydrocarbyl phosphate is employed in the present compositions in amounts of from 0.005 to 10% by weight, preferably from 0.01 to 3% based on the total composition weight. The amine salt of the monohaloalkylphosphonic acid can be used in amounts of from 0.005% to 10% by weight, but preferably is employed in the amounts of from 0.01 to 2% by composition weight. The dicarboxylic acid constituent is generally present in quantities of from 0.001 to 2% by weight, preferably from 0.005 to 0.1% by composition weight.

Other additives can also be incorporated into the compositions according to the invention. Examples of such additives are viscosity index improvers, e.g. methacrylate polymers and copolymers; antioxidants, e.g. aryl amines, phosphorous compounds or phenolic compounds; and corrosion inhibitors, antifoam agents, detergents or any other additive recognized in the art to perform a particular function or functions.

The invention will be further described by means of the following examples. It should be understood, however, that these examples are given for illustrative purposes only and the invention in its broader aspects is not limited thereto.

EXAMPLE I TABLE I Additive Base oil Coniposition:

NOTES- Additives:

Additive A=C1s22 tertiary alkyl primary amino salt of monochloromethylphosphonic acid.

Additive B =Tricresyi phosphate.

Additive C=Azelaie acid.

Base Oils:

Base Oil P=Mixed C4-1o acid esters of pentacrythritol and dipentacrythritoi containing 2.5% w. of amine antioxidants, 0.1% w. of triazole corrosion inhibitors, 0.25% \v. of a copolymerie dispersant and 10 p.p.n1. silicone fluid antii'oamant.

Base Oil Q=Base oil P minus 0.025% w. triazolc corrosion inhibitor.

Base Oil R=Base 011 P plus 0.5% W. amine antioxidant.

Base 011 S=Mixed 04-10 acid esters of pcntaerythritol and dipeutaerythritol containing 2.5% w. of amine antioxidants, 1% w. of a phenothiazine antioxidant, 1.0% W. at a phosphorothionate compound, 0.1% w. of triazole corrosion inhibitors and 10 p.p.m. silicone fluid antifoamant.

Base Oil T=Base Oil S minus 0.05% w. triazole corrosion inhibitor.

Base Oil U=Base 011 T minus 0.5% w. amine antioxidant.

Base Oil V=Base Oil 8 plus 1% W. of the amine antioxidants,

111111118 the phosphorothionate compound.

EXAMPLE II To demonstrate the effectiveness of the additive combination of the invention in reducing steel corrosion and in improving the oxidation resistance of ester base lubricants, Compositions VII, VIII, IX, and X were subjected to a Bearing Rig test under Type 1 /2 conditions as set forth in US. Military Specification MIL-L-23 6-99. Specification limits and test results are recorded in the following table.

In addition, the aforementioned compositions were evaluated by means of the new Thermal Stability-Corrosivity Test which is set forth as part of the proposed TABLE II MIL-L-23699-B U.S. Navy Specification. Results of these Composition tests are presented in the following tabulation. Bearing Big Test, 100 hrs. MIL-L-23699 Typelandl Limits VII VIII IX X Bearing (lei-merit rating 10.7 12.0 3 6.8 Overall demerit rating 80 max 36.6 38.6 16 19.2 Filter deposits, g... 3.0 max 0. 63 0. 72 0.80 0.78 Viscosity change, 100 F TABLE IV percent 5to +25.. 228.? 114.4 24.3 22.7 Acid number change- 2.0 max 7. 54 6. 98 0.52 0.58 Composition Oil consumption, ml 2,000 max 2,089 2,103 970 1, 540 Soluble iron content, p.p.m 366 174 2.9 6.3 Test procedure III IV V VI Ryder Gear Test, load-carrying capac- 2 330 s 750 The foregoing data clearly illustrate the surprising ad- A sldem 2:420 3:250 vantages of the inventive compositions (Compositions IX Relative rating p 3 ,3 and X) over those containing an acid-amine salt alone Naval Thermal Stability-Corrosivity (Composition VII), or a combination of an acid-amine gig fi g fifi g ig L2 11.5 salt with a triaryl phosphate (Composition VIII). While Viscosity increase, percent 2.2 Nil Composition VIII does have somewhat improved proper- TAN'E increase ties in respect to wiscosity index change and soluble iron 1 Sample exploded. content, it can be seen that Compositions IX and X containing the additive combination of the invention are markedly superior to the other compositions tested. This diiference exceeds that which would the expected by taking a sum of the individual additives performances, in- The datfl 0f T m further lllllstfate 1I1feaed dicating that there is a beneficial coaction between the load'cal'rylng l y deflved from the Pi c021611011 three additives which contributes to the unexpected propof the Present addltlves- Although Addltlves B and C erties not impart any significant extreme pressure properties to EXAMPLE 1 C'JIfilPOSitOIl III and IV, tliely markgdly iinproiie tle loada i'ty o omposition pro ucing a 0a -carry- In Table III priesented results further Soluble ing-capacity nearly equivalent to that of Composition content determmanons on F I and H after IV which contains six times more of extreme pressure Ada Series of nine Type g. Rlg test runs ditive A than does Composition VI. Compositions IV and shown are the load-carrying capacities of these composi- V exploded during the Naval Thermal stability cor Hons as i f' by of the Ryder Gear test rosivity test indicating acid-amine salts or azelaic acid complete description of this latter test may be found in individually do not impart the requisite Stabi1ity cor ASTM Bunetm September 1952' rosivity properties to ester base compositions. When these additives are used in combination with a trihydrocarbyl TABLE In phosphate, however, a significantly improved product results, possessing excellent extreme-pressure, thermal stacomPosmm bility and anticorrosivity properties. Test mootedre I II We claim as our invention: igtstssitstatrfttziniassatsritai .37 .2 45 A i gg ti F t ma or amoun o a syn e c car xy 1c aci es er u n- Ryder Gear Test, load carrying capacity, lbs/in 3, 640 3, 055 eating Oil and (i) from 0.005 to 10% by Weight of a tri-C hydrocarbyl phosphate, (2) from 0.005 to 10% by weight of a salt of a C primary or secondary alkyl The relatively low coPcentl'atlon of flhssolvqd m amine and a monohaloalkylphosphonic acid, wherein the Composition II prepared in accordance with the inventio haloalkyl radical contains from 1 to 4 carbon atoms, and as compared to Composition I containing only an acid- (3) from ()()1 t 2% by weight of an aliphatic dicaramine salt, is a further indication of effectiveness of the boxylic acid having from 4 to 14 carbon atoms present compositions in preventing steel corrosion. The 2 The composition of claim'l wherein the h h p osp ate Ryder Gear Test reslilts g gi gg. ihere 1 a compound is selected from the group consisting of triarylcomPleniemary reactlon etweel} e a {fives e 5 phosphates and trialkaryl phosphates, said aryl and m i f to load'canyilig capaclty' This Is evialkaryl groups having from 1 to 10 carbon atoms each. dent since Addltlv? and Addmve C by themsekes do 3. The composition of claim 2 wherein the acid-amine P2}. 3 m glgmficant aim/Hy as salt is the saltof a monochloroalkylphosphonic acid and i gz h 2 5 2 3 31 g g g g zfi z an amine selected from the group consisting of primary amines and secondary amines having from 12 to 24 carsubstantial increase in load-carrying exceeding that of bons per molecule ggililiiosition I containing a larger amount of Additive A The cfmpositionl f claim 1 h ein the phosphate EXAMPLE IV compound is present in the amount of from 0.01 to 3% by weight, the acid-amine salt is present in the amount To demonstrate further the efiicacy of the present addiof from 0.01 to 2% by weight and the dicarboxylic acid tive combination in improving the load-carrying properties is present in the amount of from 0.01 to 1% by weight. of ester base fluids, Compositions III, IV, V, and VI were 5. The composition of claim 4 wherein the ester lubrialso subjected to the Ryder Gear test. Compositions [[H, cating oil is an ester of monocarboxylic acid having 4 to IV, and V contained equal concentrations of Additive A, 14 carbon atoms and a polyalcohol selected from the B, and C respectively, while composition VI prepared in group consisting of pentaerythritol, dipentaerythritol, triaccordance with the invention contained an equal total methylolpropane and mixtures thereof. concentration, i.e., 1.22% w., of the combined additives. 6. The composition of claim 5 wherein the phosphate The base oils used in the preparation of these blends were compound is tricresyl phosphate. identical.

7. The composition of claim 6 wherein the acid-amine 9. The composition of claim 8 wherein the ester base 5 oil is a mixture of C monocarboxylic acid esters of pentaerythritol and dipentaerythritol.

References Cited UNITED STATES PATENTS 2,858,332 10/1958 Watson et a1 252--32.5 X 2,938,871 5/1960 Matuszak et al 252-499 8 12/1964 Price et a1. 252--32.5 X 4/1970 Thompson 252-565 OTHER REFERENCES Egan, Lubrication Eingineering March-February 1947, pp. 24, 25 and26.

DANIEL E. WYMAN, Primary Examiner W. H. CANNON, Assistant Examiner U.S. Cl. X.R. 25234.7 

